Aluminum alloy feedstocks for additive manufacturing

ABSTRACT

Some variations provide an aluminum alloy feedstock for additive manufacturing, the aluminum alloy feedstock comprising from 81.5 wt % to 88.8 wt % aluminum; from 1.1 wt % to 2.1 wt % copper; from 3.0 wt % to 4.6 wt % magnesium; and from 7.1 wt % to 9.0 wt % zinc. The aluminum alloy feedstock may be in the form of a free-flowing powder or a feedstock ingot, for example. In some variations, the aluminum alloy feedstock comprises from 84.9 wt % to 88.3 wt % aluminum; from 1.2 wt % to 2.0 wt % copper; from 3.2 wt % to 4.4 wt % magnesium; and from 7.3 wt % to 8.7 wt % zinc.

PRIORITY DATA

This patent application is continuation-in-part application of U.S.patent application Ser. No. 16/262,891, filed on Jan. 30, 2019, which isa continuation-in-part application of U.S. patent application Ser. No.16/180,696, filed on Nov. 5, 2018, which in turn is a continuationapplication of U.S. patent application Ser. No. 15/996,438, filed onJun. 2, 2018, which claims priority to U.S. Provisional Patent App. No.62/540,615, filed on Aug. 3, 2017, each of which is hereby incorporatedby reference herein. This patent application is also acontinuation-in-part application of U.S. patent application Ser. No.16/223,858, filed on Dec. 18, 2018, which is a continuation patentapplication of U.S. patent application Ser. No. 15/880,466, filed onJan. 25, 2018, which claims priority to U.S. Provisional Patent App. No.62/452,989, filed on Feb. 1, 2017, each of which is hereby incorporatedby reference herein.

FIELD OF THE INVENTION

The present invention generally relates to processes for additivemanufacturing using optimized metal-containing precursors (e.g.,powders).

BACKGROUND OF THE INVENTION

Metal-based additive manufacturing, or three-dimensional (3D) printing,has applications in many industries, including the aerospace andautomotive industries. Building up metal components layer-by-layerincreases design freedom and manufacturing flexibility, thereby enablingcomplex geometries while eliminating traditional economy-of-scaleconstraints. In metal-based additive manufacturing, application of adirect energy source, such as a laser or electron beam, to melt alloypowders locally results in solidification rates between 0.1 m/s and 5m/s, an order of magnitude increase over conventional casting processes.

Additive manufacturing allows for one-step fabrication of complex partsof arbitrary design. Additive manufacturing eliminates the need forassembling multiple components or setting up new equipment, whileminimizing manufacturing time and wastage of materials and energy.Although additive manufacturing is rapidly growing to produce metallic,polymeric, and ceramic components, production of metallic parts is itsfastest growing sector.

In order to successfully print a metallic part, an appropriate alloymust be selected. Successive layers need to be adequately bonded byfusion. An understanding of printability, including the ability of analloy to resist distortion and fusion defects, is important for powderbed—based additive manufacturing processes.

Currently only a few alloys, the most relevant being AlSi10Mg, TiAl6V4,CoCr, and Inconel 718, can be reliably additively manufacturing. Thevast majority of the more than 5,500 alloys in use today cannot beadditively manufactured because the melting and solidification dynamicsduring the printing process lead to intolerable microstructures withlarge columnar grains and cracks. 3D-printable metal alloys are limitedto those known to be easily weldable. The limitations of the currentlyprintable alloys, especially with respect to specific strength, fatiguelife, and fracture toughness, have hindered metal-based additivemanufacturing. See Martin et al., “3D printing of high-strengthaluminium alloys” Nature vol. 549, pages 365-369.

Specifically regarding aluminum alloys, for example, the only printablealuminum alloys are based on the binary Al—Si system and tend toconverge around a yield strength of approximately 200 MPa with a lowductility of 4%. The exception is Scalmalloy, which relies on alloyingadditions of scandium, a rare high-cost metal. In contrast, mostaluminum alloys used in automotive, aerospace, and consumer applicationsare wrought alloys of the 2000, 5000, 6000, or 7000 series, which canexhibit strengths exceeding 400 MPa and ductility of more than 10% butcannot currently be additively manufactured. These systems have low-costalloying elements (Cu, Mg, Zn, and Si) carefully selected to producecomplex strengthening phases during subsequent ageing. These sameelements promote large solidification ranges, leading to hot tearing(cracking) during solidification—a problem that has been difficult tosurmount for more than 100 years since the first age-hardenable alloy,duralumin, was developed.

In particular, during solidification of these alloys, the primaryequilibrium phase solidifies first at a different composition from thebulk liquid. This mechanism results in solute enrichment in the liquidnear the solidifying interface, locally changing the equilibriumliquidus temperature and producing an unstable, undercooled condition.As a result, there is a breakdown of the solid—liquid interface leadingto cellular or dendritic grain growth with long channels ofinterdendritic liquid trapped between solidified regions. As temperatureand liquid volume fraction decrease, volumetric solidification shrinkageand thermal contraction in these channels produces cavities and hottearing cracks which may span the entire length of the columnar grainand can propagate through additional intergranular regions. Note thataluminum alloys Al 7075 and Al 6061 are highly susceptible to theformation of such cracks, due to a lack of processing paths to producefine equiaxed grains.

Another problem associated with additive manufacturing of metals is thatproducing equiaxed structures typically requires large amounts ofundercooling, which has thus far proven difficult in additive processeswhere high thermal gradients arise from rastering of a direct energysource in an arbitrary geometric pattern. Fine equiaxed microstructuresaccommodate strain in the semi-solid state by suppressing coherency thatlocks the orientation of these solid dendrites and promotes tearing.

Yet another problem associated with additive manufacturing of metalsarises from the vapor pressures of some metals themselves. Mostengineering alloys contain multiple alloying elements that vaporizerapidly at high temperatures and can be selectively lost during additivemanufacturing or welding. Consequently, the chemical composition of thefinal part may be different from that of the original material.

In particular, at high temperatures encountered during additivemanufacturing, significant vaporization of alloying elements can happenout of the melt pool. Since some alloying elements are more volatilethan others, selective vaporization of alloying elements often resultsin a significant change in the composition of the alloy. For example,during laser welding of aluminum alloys, losses of magnesium and zincresult in pronounced changes to their concentrations. The compositionchange can cause degradation of mechanical properties (e.g., tensilestrength) and chemical properties (e.g., corrosion resistance) in thefinal structure.

A reduction in peak temperature and a smaller surface-to-volume ratio ofthe melt pool may minimize pronounced changes of chemical compositionduring laser processing. However, it is not always possible to minimizetemperature due to the presence of high-melting-point metals that needto be liquefied during additive manufacturing. Likewise, depending onthe specific additive manufacturing set-up or three-dimensional objectto be printed, it is not always possible to reduce surface-to-volumeratio of the melt pool—or even if that can be done, it may not besufficient to prevent significant vaporization of high-vapor-pressuremetals.

A lack of teaching in the art with respect to processing of alloysystems that undergo vaporization makes it very difficult to selecttargeted alloy feedstock compositions. Currently, metal powders andfeedstocks are produced at the same composition as the desired finalalloy. There is a need to provide optimized feedstocks for additivemanufacturing of metals, to address this significant problem.

SUMMARY OF THE INVENTION

The present invention addresses the aforementioned needs in the art, aswill now be summarized and then further described in detail below.

Some variations provide an aluminum alloy feedstock for additivemanufacturing, the aluminum alloy feedstock comprising:

from 81.5 wt % to 88.8 wt % aluminum;

from 1.1 wt % to 2.1 wt % copper;

from 3.0 wt % to 4.6 wt % magnesium; and

from 7.1 wt % to 9.0 wt % zinc.

In some embodiments, the aluminum alloy feedstock is in the form of afree-flowing powder, which may be referred to as an ingot. In someembodiments, the aluminum alloy feedstock is in the form of an ingotthat is not a loose powder.

In various embodiments, the aluminum alloy feedstock comprises from0.005 wt % to 0.4 wt % silicon or from 0.005 wt % to 0.12 wt % silicon.The aluminum alloy feedstock may contain 0 wt % silicon.

In various embodiments, the aluminum alloy feedstock comprises from0.005 wt % to 0.4 wt % iron or from 0.005 wt % to 0.15 wt % iron. Thealuminum alloy feedstock may contain 0 wt % iron.

In various embodiments, the aluminum alloy feedstock comprises from0.005 wt % to 0.3 wt % manganese or from 0.005 wt % to 0.1 wt %manganese. The aluminum alloy feedstock may contain 0 wt % manganese.

In various embodiments, the aluminum alloy feedstock comprises from0.005 wt % to 0.1 wt % chromium or from 0.005 wt % to 0.05 wt %chromium. The aluminum alloy feedstock may contain 0 wt % chromium.

In various embodiments, the aluminum alloy feedstock comprises from0.005 wt % to 0.05 wt % nickel or from 0.005 wt % to 0.05 wt % nickel.The aluminum alloy feedstock may contain 0 wt % nickel.

In various embodiments, the aluminum alloy feedstock comprises from0.005 wt % to 0.2 wt % titanium or from 0.005 wt % to 0.1 wt % titanium.The aluminum alloy feedstock may contain 0 wt % titanium.

In various embodiments, the aluminum alloy feedstock comprises from0.005 wt % to 0.05 wt % tin or from 0.005 wt % to 0.05 wt % tin. Thealuminum alloy feedstock may contain 0 wt % tin.

In some variations, the aluminum alloy feedstock comprises:

from 84.9 wt % to 88.3 wt % aluminum;

from 1.2 wt % to 2.0 wt % copper;

from 3.2 wt % to 4.4 wt % magnesium; and

from 7.3 wt % to 8.7 wt % zinc.

In some variations, the aluminum alloy feedstock consists essentially ofthe aluminum, the copper, the magnesium, and the zinc. Other minorcomponents (e.g., impurities) may be present at a total concentrationless than 0.25 wt %, preferably less than 0.15 wt %, with individualminor components each less than 0.05 wt %. In certain embodiments, thealuminum alloy feedstock consists of the aluminum, the copper, themagnesium, and the zinc, without other components present.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic illustration of the vaporization ofhigh-vapor-pressure metals during additive manufacturing, in someembodiments.

FIG. 2 is an exemplary method flowchart for producing an additivelymanufactured metal component, in some embodiments.

FIG. 3 shows an SEM image of additively manufactured, grain-refinedaluminum alloy Al 6061 with Zr particles, revealing fine equiaxed grainsand a substantially crack-free microstructure, in some embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The compositions, structures, systems, and methods of the presentinvention will be described in detail by reference to variousnon-limiting embodiments.

This description will enable one skilled in the art to make and use theinvention, and it describes several embodiments, adaptations,variations, alternatives, and uses of the invention. These and otherembodiments, features, and advantages of the present invention willbecome more apparent to those skilled in the art when taken withreference to the following detailed description of the invention inconjunction with the accompanying drawings.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contextclearly indicates otherwise. Unless defined otherwise, all technical andscientific terms used herein have the same meaning as is commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs.

Unless otherwise indicated, all numbers expressing conditions,concentrations, dimensions, and so forth used in the specification andclaims are to be understood as being modified in all instances by theterm “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that may vary depending at least upona specific analytical technique.

The term “comprising,” which is synonymous with “including,”“containing,” or “characterized by” is inclusive or open-ended and doesnot exclude additional, unrecited elements or method steps. “Comprising”is a term of art used in claim language which means that the named claimelements are essential, but other claim elements may be added and stillform a construct within the scope of the claim.

As used herein, the phrase “consisting of” excludes any element, step,or ingredient not specified in the claim. When the phrase “consists of”(or variations thereof) appears in a clause of the body of a claim,rather than immediately following the preamble, it limits only theelement set forth in that clause; other elements are not excluded fromthe claim as a whole. As used herein, the phrase “consisting essentiallyof” limits the scope of a claim to the specified elements or methodsteps, plus those that do not materially affect the basis and novelcharacteristic(s) of the claimed subject matter.

With respect to the terms “comprising,” “consisting of,” and “consistingessentially of,” where one of these three terms is used herein, thepresently disclosed and claimed subject matter may include the use ofeither of the other two terms, except when used in Markush groups. Thusin some embodiments not otherwise explicitly recited, any instance of“comprising” may be replaced by “consisting of” or, alternatively, by“consisting essentially of.”

During additive manufacturing of metals, a direct energy source locallymelts metal or metal alloy feedstocks and builds up a part, layer bylayer. During this process, intense heating can vaporizehigh-vapor-pressure metals, depending on temperatures and mass-transportpathways. A simple illustration is shown in FIG. 1, described below.Vaporization of metals from the melt pool results in a material that,after solidification, is a different composition compared to thestarting feedstock. In many cases, this means that the resultingstructure is no longer the correct composition. As used herein, “meltpool” refers to a volume of molten metal that is formed during additivemanufacturing or welding.

Variations of the present invention are premised on providing afeedstock with enriched high-vapor-pressure metals, so that the finaladditively manufactured structure contains a targeted composition. Thetargeted composition, which differs from the feedstock composition, isvery important to the final material properties.

For example, during additive manufacturing of aluminum alloy Al 7075powders, about 30% of the magnesium and about 25% of the zinc can belost during the additive manufacturing process. These elements have highvapor pressures in the melt pool, which can reach temperatures exceeding1000° C. At these temperatures, the vapor pressure of Mg and Zn are muchhigher than 1 kPa—specifically, about 40 kPa for Mg and over 100 kPa forZn (1 kPa=0.01 bar). Other elements in the alloy, such as copper andchromium, are relatively unchanged due to their negligible vaporpressures at additive manufacturing temperatures. Theselow-vapor-pressure metals have minor concentration enrichment from theassociated mass loss of the high-vapor-pressure elements.

Heretofore, there are no available aluminum alloy feedstocks containinghigh levels of high-vapor-pressure elements such as Mg, Zn, and Li, thatwill result in an additively manufactured structure of identicalcomposition to the original powder. Variations of this invention enablethe production of additively manufactured high-strength metal alloyswith targeted compositions that contain high-vapor-pressure elements.

Some variations provide a method of making an additively manufacturedmetal component, the method comprising:

(a) providing a metal-containing feedstock comprising ahigh-vapor-pressure metal and at least one other metal species differentthan the high-vapor-pressure metal;

(b) exposing a first amount of the metal-containing feedstock to anenergy source for melting the first amount of the metal-containingfeedstock, thereby generating a first melt layer; and

(c) solidifying the first melt layer, thereby generating a first solidlayer of an additively manufactured metal component,

wherein the metal-containing feedstock contains a higher concentrationof the high-vapor-pressure metal compared to the concentration of thehigh-vapor-pressure metal in the first solid layer.

Steps (b) and (c) may be repeated a plurality of times to generate aplurality of solid layers by sequentially solidifying a plurality ofmelt layers in an additive-manufacturing build direction.

In this disclosure, a “metal-containing feedstock” is anymetal-containing powder, wire, sheet, or other geometric object of anycompatible size that can be utilized in additive manufacturing orwelding processes. The additive manufacturing or welding processes mayemploy conventional equipment or customized apparatus suitable forcarrying out the methods taught herein to produce an additivelymanufactured or welded metal component. By “component” it is meant anyobject that is produced by additive manufacturing, 3D printing, orwelding.

A simple illustration is shown in FIG. 1. In the schematic of FIG. 1, ametal-containing powder feed 110 is exposed to an energy source 120,melting the powder to form a melt pool 130. Solidification of the meltpool results in a work piece 140, which may contain one or moreindividual layers of solidified metal-containing feedstock.High-vapor-pressure metals 150 may vaporize from the melt pool 140, asdepicted by the serpentine arrows of FIG. 1. The energy source 120and/or the work piece 140 may be moved in a prescribed pattern to buildthe desired work piece 140. In some embodiments, a wire feed isemployed, rather than a powder feed. In other embodiments, a powder bedis employed, in which the energy source melts metal-containing powderthat is disposed as a layer on the work piece 140. In any of thesescenarios, a melt pool 130 forms, from which high-vapor-pressure metals140 may be vaporized and released to a space outside of the work area.Note that the serpentine arrows showing vaporizing metals 150 areintended to be outside of the work piece 140, not within it.Notwithstanding the foregoing, some vaporizing metal atoms may penetratethrough the solidifying work piece 140 or may be temporarily containedwithin vapor-containing porous regions of the work piece 140, beforebeing released out of the system of FIG. 1.

The metal-containing feedstock includes a base metal (such as, but notlimited to, aluminum) and one or more additional elements, to form ametal alloy. In various embodiments, at least one additional element, ora plurality of additional elements, is present in a concentration fromabout 0.01 wt % to about 20 wt %, such as about 0.1, 0.5, 1.0, 1.5, 2,3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 wt %. In this disclosure,at least one of the additional elements is a high-vapor-pressure metal.

In some embodiments, one or more metals are selected from the groupconsisting of aluminum, iron, nickel, copper, titanium, magnesium, zinc,silicon, lithium, silver, chromium, manganese, vanadium, bismuth,gallium, lead, and combinations thereof. The metal-containing feedstockmay contain one or more alloying elements selected from the groupconsisting of Al, Si, Fe, Cu, Ni, Mn, Mg, Cr, Zn, V, Ti, Bi, Ga, Pb, orZr. Other alloying elements may be included in the metal-containingfeedstock, such as (but not limited to) H, Li, Be, B, C, N, O, F, Na, P,S, Cl, K, Ca, Sc, Co, Zn, Ga, Ge, As, Se, Br, Rb, Sr, Y, Nb, Mo, Tc, Ru,Rh, Pd, Ag, Cd, In, Sn, Te, I, Cs, Ba, Hf, Ta, W, Re, Os, Ir, Pt, Au,Hg, Tl, Ce, Nd, and combinations thereof. These other alloying elementsmay function as grain refiners, as strength enhancers, as stabilityenhancers, or a combination thereof.

The high-vapor-pressure metal, or a combination of high-vapor-pressuremetals, may be present in the metal-containing feedstock in aconcentration from about 0.1 wt % to about 20 wt %, for example. Invarious embodiments, the high-vapor-pressure metal, or a combination ofhigh-vapor-pressure metals, may be present in the metal-containingfeedstock in a concentration of about 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10wt %, or higher. When multiple high-vapor-pressure metals are present,the individual high-vapor-pressure metals may each be present in themetal-containing feedstock in a concentration of about 0.1, 0.5, 1, 2,3, 4, 5, 6, 7, 8, 9, 10 wt %, or higher.

A “high-vapor-pressure metal” as meant herein includes a metal that hasa vapor pressure of 1 kPa or greater at a melt-pool temperature. A“high-vapor-pressure metal” also includes a metal for which at least 1%by mass is lost to a vapor phase or the atmosphere from a multicomponentsolution, at a melt-pool temperature, during an additive manufacturingor welding process.

A “melt-pool temperature” refers to a temperature that characterizes amelt pool, which temperature may be a melt-pool volume-averagetemperature, a melt-pool time-average temperature, a melt-pool surfacetemperature, or a melt-pool peak temperature (the highest temperaturereached by any surface or region within the melt pool). For a melt-pooltime-average temperature, the time is the time span for the creation andsolidification of a melt pool in an additive manufacturing or weldingprocess. A melt-pool temperature may also be an overall averagetemperature, averaged over both space and time.

A melt-pool temperature will vary depending at least on the specificmetals to be melted, the power intensity applied to the melt pool, andthe geometry of the melt pool. A melt-pool temperature may vary fromabout 800° C. to about 2000° C., such as about, or at least about, 900°C., 1000° C., 1100° C., 1200° C., 1300° C., 1400° C., 1500° C., 1600°C., 1700° C., 1800° C., or 1900° C., for example, noting that thesetemperatures may be volume-average temperatures, time-averagetemperatures, surface temperatures, and/or peak temperatures of the meltpool. In various embodiments, a selected high-vapor-pressure metal has avapor pressure of 1 kPa or greater at 1000° C., 1100° C., 1200° C.,1300° C., 1400° C., 1500° C., 1600° C., 1700° C., or 1800° C.

In some embodiments, a selected high-vapor-pressure metal has a vaporpressure of 5 kPa, 10 kPa, 20 kPa, 30 kPa, 40 kPa, 50 kPa, 60 kPa, 70kPa, 80 kPa, 90 kPa, 100 kPa or greater at a melt-pool temperature. Insome embodiments, a selected high-vapor-pressure metal has a vaporpressure of 1 kPa or greater at a temperature less than a melt-pooltemperature, such as about 100° C., 200° C., 300° C., 400° C., or 500°C. less than the melt-pool temperature.

The high-vapor-pressure metal may be selected from the group consistingof Mg, Zn, Li, Al, Cd, Hg, K, Na, Rb, Cs, Mn, Be, Ca, Sr, Ba, andcombinations thereof. In certain embodiments, the high-vapor-pressuremetal is selected from the group consisting of Mg, Zn, Al, Li, andcombinations thereof.

Aluminum at 1000° C. has a single-component vapor pressure of about3×10⁻⁵ kPa but is experimentally observed to be volatile during additivemanufacturing. Even when average melt-pool temperatures are around 1000°C., local hot spots are believed to reach at least 1700° C., at whichthe vapor pressure of Al exceeds 1 kPa. Therefore, Al is ahigh-vapor-pressure metal, in some embodiments.

The other metal species different than the high-vapor-pressure metal maybe classified as a low-vapor-pressure metal, such as (but not limitedto) transition metals. Exemplary low-vapor-pressure metals include Cu,Ni, Cr, W, and Mo. A “low-vapor-pressure metal” as meant herein is ametal that has a vapor pressure less than 1 kPa at a melt-pooltemperature. The vapor pressure of a selected low-vapor-pressure metalmay be significantly lower than 1 kPa, such as about 10⁻³ kPa, 10⁻⁴ kPa,10⁻⁵ kPa, 10⁻⁶ kPa, 10⁻⁷ kPa, 10⁻⁸ kPa, 10⁻⁹ kPa, or 10⁻¹⁰ kPa, orlower, at a melt-pool temperature.

Note that for some metals with vapor pressures below 1 kPa at amelt-pool temperature, those metals may nevertheless be lost to asignificant extent from the solid component as it is being formed duringadditive manufacturing or welding. This can occur for several reasons.First, non-ideal multicomponent solution thermodynamics may cause ametal to vaporize at a temperature different than its pure(single-component) vaporization temperature for a given pressure.Second, the specific atmosphere (e.g., presence of inert gases orreactive gases) above the metal solution may alter the vaporizationthermodynamics. Third, localized hot spots can occur during additivemanufacturing or welding, causing localized regions of higher vaporpressure for a metal. Finally, in some cases a metal may be entrained orotherwise carried into a vapor phase despite being nominally a solid atthe given temperature and pressure. A metal that transports into a vaporphase for any reason is considered to be vaporized, in this disclosure.

Generally, the specific extents of metal vaporization are dictated bythe original (feedstock) composition and the associated solvationenergies keeping the alloying elements in solution. These extents ofmetal vaporization can be experimentally determined and/or predicted bycalculations or simulations. With that information, alloy systems can beoptimized to accommodate the expected mass loss of thehigh-vapor-pressure elements.

In some embodiments, simulations are employed to estimate extents ofmetal vaporization in complex multicomponent metal solutions. Thesesimulations may account for variations in temperatures, laser powerintensity, pressures and pressure gradients, time, mass-transportpathways and concentration gradients, heat transfer (by conduction,convection, and radiation), 3D geometry, surface tension, buoyancyforces, and/or diluent gases, among other potential factors.

The simulations may be configured to predict both formal vaporization ofmetals as well as entrainment, such as ejection of tiny metal dropletsowing to the recoil force exerted by metal vapors. These simulations mayinclude calculations to solve for the temperature and velocity fieldsduring additive manufacturing or welding, using a transient, heattransfer and fluid flow model based on the solution of the equations ofconservation of mass, momentum, and energy in the melt pool. Simulationsoftware may be utilized, such as ANSYS Fluent (Canonsburg, Pa., US), toassist in the calculations. Fuerschbach et al., “Understanding MetalVaporization from Laser Welding” Sandia National Laboratories Report No.SAND2003-3490, 2003, is hereby incorporated by reference herein for itsexemplary teachings of theoretical considerations in simulating extentsof metal vaporization in embodiments herein.

The specific extents of metal vaporization may alternatively, oradditionally, be determined experimentally. For example, in the case ofadditive manufacturing of aluminum alloy Al 7075 powders, it has beenexperimentally found that, under certain conditions, about 25% of zincand about 30% of magnesium are lost during fabrication of the 3D-printedcomponent. This information can be utilized in future additivemanufacturing processes and simulations for Al 7075 alloys.

The enrichment ratio of wt % concentration of the high-vapor-pressuremetal in the metal-containing feedstock to wt % concentration of thehigh-vapor-pressure metal in the first solid layer is typically at least1.05, such as at least 1.25, at least 1.5, or at least 2.0. Whenmultiple layers are produced, the enrichment ratio of wt % concentrationof the high-vapor-pressure metal in the metal-containing feedstock to wt% concentration of the high-vapor-pressure metal in each additionalsolid layer is typically at least 1.05, such as at least 1.25, at least1.5, or at least 2.0. In various embodiments, the enrichment ratio of acertain high-vapor-pressure metal, in one or more solid layers, isabout, or at least about, 1.01, 1.02, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3,1.35, 1.4, 1.45, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5,2.6, 2.7, 2.8, 2.9, or 3.0. The enrichment ratios of individual elementswill generally be different due to differences in properties ofelements. Elements with higher vapor pressures will tend to have higherenrichment ratios.

The enrichment ratios for a given element may be about the same in allsolid layers, when additive manufacturing conditions remain constant inthe build direction. In some embodiments, the enrichment ratios for agiven element may vary by build layer, such as when local temperature,heating/cooling profile, pressure, or gas atmosphere varies at least tosome extent in the additive manufacturing build direction.

In some embodiments, the metal-containing feedstock contains from 0.05wt % to 0.28 wt % Cr, from 1 wt % to 2 wt % Cu, from 3 wt % to 10 wt %Mg, and from 6.2 wt % to 20 wt % Zn; and wherein the first solid layercontains from 0.18 wt % to 0.28 wt % Cr, from 1.2 wt % to 2 wt % Cu,from 2.1 wt % to 2.9 wt % Mg, and from 5.1 wt % to 6.1 wt % Zn. Theenrichment ratios of Cr, Cu, Mg, and/or Zn may vary, such as at least1.05, at least 1.25, at least 1.5, or at least 2.0, noting that theenrichment ratios of individual elements will generally be different dueto differences in properties of elements.

In some embodiments, the metal-containing feedstock contains from 0.01wt % to 5 wt % Zr, from 1 wt % to 2.6 wt % Cu, from 2.7 wt % to 10 wt %Mg, and from 6.7 wt % to 20 wt % Zn; and wherein the first solid layercontains from 0.08 wt % to 5 wt % Zr, from 2 wt % to 2.6 wt % Cu, from1.9 wt % to 2.6 wt % Mg, and from 5.7 wt % to 6.7 wt % Zn. Theenrichment ratios of Zr, Cu, Mg, and/or Zn may vary, such as at least1.05, at least 1.25, at least 1.5, or at least 2.0, for example.

In some embodiments, the metal-containing feedstock contains from 0.01wt % to 5 wt % Zr, from 1.9 wt % to 10 wt % Mg, and from 7.1 wt % to 20wt % Zn; and wherein the first solid layer contains from 0.07 wt % to 5wt % Zr, from 1.3 wt % to 1.8 wt % Mg, and from 7 wt % to 8 wt % Zn. Theenrichment ratios of Zr, Mg, and/or Zn may vary, such as at least 1.05,at least 1.25, at least 1.5, or at least 2.0, for example.

Some variations provide an aluminum alloy feedstock for additivemanufacturing, the aluminum alloy feedstock comprising:

from 81.5 wt % to 88.8 wt % aluminum;

from 1.1 wt % to 2.1 wt % copper;

from 3.0 wt % to 4.6 wt % magnesium; and

from 7.1 wt % to 9.0 wt % zinc.

In some embodiments, the aluminum alloy feedstock is in the form of apowder, which may be referred to as an ingot. Other ingot geometries(besides a loose powder) may be provided, such as wires, cylinders,rods, spheres, etc.

In various embodiments, the aluminum alloy feedstock comprises from0.005 wt % to 0.4 wt % silicon or from 0.005 wt % to 0.12 wt % silicon.The aluminum alloy feedstock may contain 0 wt % silicon, or nodetectible silicon.

In various embodiments, the aluminum alloy feedstock comprises from0.005 wt % to 0.4 wt % iron or from 0.005 wt % to 0.15 wt % iron. Thealuminum alloy feedstock may contain 0 wt % iron, or no detectable iron.

In various embodiments, the aluminum alloy feedstock comprises from0.005 wt % to 0.3 wt % manganese or from 0.005 wt % to 0.1 wt %manganese. The aluminum alloy feedstock may contain 0 wt % manganese, orno detectable manganese.

In various embodiments, the aluminum alloy feedstock comprises from0.005 wt % to 0.1 wt % chromium or from 0.005 wt % to 0.05 wt %chromium. The aluminum alloy feedstock may contain 0 wt % chromium, orno detectable chromium.

In various embodiments, the aluminum alloy feedstock comprises from0.005 wt % to 0.05 wt % nickel or from 0.005 wt % to 0.05 wt % nickel.The aluminum alloy feedstock may contain 0 wt % nickel, or no detectiblenickel.

In various embodiments, the aluminum alloy feedstock comprises from0.005 wt % to 0.2 wt % titanium or from 0.005 wt % to 0.1 wt % titanium.The aluminum alloy feedstock may contain 0 wt % titanium, or nodetectible titanium.

In various embodiments, the aluminum alloy feedstock comprises from0.005 wt % to 0.05 wt % tin or from 0.005 wt % to 0.05 wt % tin. Thealuminum alloy feedstock may contain 0 wt % tin, or no detectible tin.

In some embodiments, the aluminum alloy feedstock comprises from 0.005wt % to 0.4 wt % or from 0.005 wt % to 0.12 wt % silicon, from 0.005 wt% to 0.4 wt % or from 0.005 wt % to 0.15 wt % iron, from 0.005 wt % to0.3 wt % or from 0.005 wt % to 0.1 wt % manganese, from 0.005 wt % to0.1 wt % or from 0.005 wt % to 0.05 wt % chromium, from 0.005 wt % to0.05 wt % or from 0.005 wt % to 0.05 wt % nickel, from 0.005 wt % to 0.2wt % or from 0.005 wt % to 0.1 wt % titanium, and from 0.005 wt % to0.05 wt % or from 0.005 wt % to 0.05 wt % tin.

In some embodiments, the aluminum alloy feedstock comprises:

from 84.9 wt % to 88.3 wt % aluminum;

from 1.2 wt % to 2.0 wt % copper;

from 3.2 wt % to 4.4 wt % magnesium; and

from 7.3 wt % to 8.7 wt % zinc.

In some embodiments, the aluminum alloy feedstock comprises:

about 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, or 90 wt % aluminum, or arange from one to another of these values;

about 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or 2.1 wt %copper, or a range from one to another of these values;

about 3.0, 3.1, 3.2, 3.3. 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2,4.3, 4.4, 4.5, or 4.6 wt % magnesium, or a range from one to another ofthese values; and/or

about 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3,8.4, 8.5, 8.6, 8.7, 8.8, 8.9, or 9.0 wt % zinc, or a range from one toanother of these values.

In some variations, the aluminum alloy feedstock consists essentially ofthe aluminum, the copper, the magnesium, and the zinc. Other minorcomponents (e.g., impurities) may be present at a total concentrationless than 0.25 wt %, preferably less than 0.15 wt %, with individualminor components each less than 0.05 wt %. In certain embodiments, thealuminum alloy feedstock consists of the aluminum, the copper, themagnesium, and the zinc, without other components present.

The aluminum alloy feedstock may function as a starting feedstock forcombining (e.g., at a later time and/or location) with a grain-refinerelement, such as (but not limited to) zirconium. The zirconium mayfunction as a grain-refiner element for an additive manufacturingprocess that starts with the zirconium-containing aluminum alloyfeedstock. In some embodiments, the zirconium is in the form ofnanoparticles. The zirconium particles may be disposed on surfaces ofthe other metals present.

The zirconium-containing aluminum alloy feedstocks may be used toproduce an additively manufactured aluminum alloy comprising:

from 84.5 wt % to 92.1 wt % aluminum;

from 1.1 wt % to 2.1 wt % copper;

from 1.8 wt % to 2.9 wt % magnesium;

from 4.5 wt % to 6.1 wt % zinc; and

from 0.5 wt % to 2.8 wt % zirconium.

The additively manufactured aluminum alloy is typically in the form of athree-dimensional component, or a portion thereof. In some embodiments,an as-built component may be referred to as a casting.

In some embodiments, the additively manufactured aluminum alloycomprises from 0.005 wt % to 0.4 wt % silicon. The additivelymanufactured aluminum alloy may contain 0 wt % silicon.

In some embodiments, the additively manufactured aluminum alloycomprises from 0.005 wt % to 0.4 wt % iron. The additively manufacturedaluminum alloy may contain 0 wt % iron.

In some embodiments, the additively manufactured aluminum alloycomprises from 0.005 wt % to 0.3 wt % manganese. The additivelymanufactured aluminum alloy may contain 0 wt % manganese.

In some embodiments, the additively manufactured aluminum alloycomprises from 0.005 wt % to 0.1 wt % chromium. The additivelymanufactured aluminum alloy may contain 0 wt % chromium.

In some embodiments, the additively manufactured aluminum alloycomprises from 0.005 wt % to 0.05 wt % nickel. The additivelymanufactured aluminum alloy may contain 0 wt % nickel.

In some embodiments, the additively manufactured aluminum alloycomprises from 0.005 wt % to 0.1 wt % titanium. The additivelymanufactured aluminum alloy may contain 0 wt % titanium.

In some embodiments, the additively manufactured aluminum alloycomprises from 0.005 wt % to 0.05 wt % tin. The additively manufacturedaluminum alloy may contain 0 wt % tin.

In some variations, the additively manufactured aluminum alloy consistsessentially of the aluminum, the copper, the magnesium, the zinc, andthe zirconium. Other minor components (e.g., impurities) may be presentat a total concentration less preferably than 0.25 wt %, with individualminor components each less than 0.05 wt %. In certain embodiments, theadditively manufactured aluminum alloy consists of the aluminum, thecopper, the magnesium, the zinc, and the zirconium, without othercomponents present.

The metal-containing feedstock, the final component, or both of thesemay be characterized as an aluminum alloy (e.g., from the 6000 series or7000 series of Al alloys), a magnesium alloy, a titanium alloy, a nickelsuperalloy, a copper superalloy, or a combination thereof. FIG. 3depicts an exemplary microstructure 300 for additively manufacturedcomponents containing aluminum alloy Al 6061, for example. FIG. 3 showsan SEM image of additively manufactured, grain-refined aluminum alloy Al6061 with Zr particles (not individually visible in FIG. 3), revealingfine equiaxed grains 310 and a substantially crack-free microstructure300 containing a few porous voids 320, in some embodiments.

A “superalloy” is an alloy that exhibits excellent mechanical strength,resistance to thermal creep deformation, good surface stability, andresistance to corrosion or oxidation. Examples of superalloys includeHastelloy, Inconel, Waspaloy, and Incoloy. Some superalloys have a γ′(gamma prime) phase, which is an intermetallic precipitate to strengthenthe superalloy. For example, in Ni-based superalloys, a γ′-Ni₃Al/Ni₃Tiphase acts as a barrier to dislocation motion. This γ′ intermetallicphase, when present in high volume fractions, drastically increases thestrength of these alloys due to the ordered nature and high coherency ofthe γ′ intermetallic phase with the continuous matrix.

In some embodiments, aluminum is present in the metal-containingfeedstock in a concentration from about 0.1 wt % to about 90 wt %. Insome embodiments, copper is present in the metal-containing feedstock ina concentration from about 0.1 wt % to about 90 wt %. In these or otherembodiments, magnesium is present in the metal-containing feedstock in aconcentration from about 0.1 wt % to about 90 wt %. In these or otherembodiments, at least one of zinc or silicon is present in themetal-containing feedstock in a concentration from about 0.1 wt % toabout 90 wt %. In some embodiments, the metal-containing feedstockfurther comprises chromium. In some embodiments, scandium is not presentin the metal-containing feedstock.

In general, the geometry of the metal-containing feedstock is notlimited and may be, for example, in the form of powder particles, wires,rods, bars, plates, films, coils, spheres, cubes, prisms, cones,irregular shapes, or combinations thereof. In certain embodiments, themetal-containing feedstock is in the form of a powder, a wire, or acombination thereof (e.g., a wire with powder on the surface). When themetal-containing feedstock is in the form of powder, the powderparticles may have an average diameter from about 1 micron to about 500microns, such as about 10 microns to about 100 microns, for example.When the metal-containing feedstock is in the form of a wire, the wiremay have an average diameter from about 10 microns to about 1000microns, such as about 50 microns to about 500 microns, for example.

The energy source in step (b) may be provided by a laser beam, anelectron beam, alternating current, direct current, plasma energy,induction heating from an applied magnetic field, ultrasonic energy,other sources, or a combination thereof. Typically, the energy source isa laser beam or an electron beam.

In various embodiments, steps (b) and (c) utilize a technique selectedfrom the group consisting of selective laser melting, electron beammelting, laser engineered net shaping, selective laser sintering, directmetal laser sintering, integrated laser melting with machining, laserpowder injection, laser consolidation, direct metal deposition,wire-directed energy deposition, plasma arc-based fabrication,ultrasonic consolidation, and combinations thereof.

In certain embodiments, the additive manufacturing process is selectedfrom the group consisting of selective laser melting, energy-beammelting, laser engineered net shaping, and combinations thereof.

Selective laser melting utilizes a laser (e.g., Yb-fiber laser) toprovide energy for melting. Selective laser melting designed to use ahigh power-density laser to melt and fuse metallic powders together. Theprocess has the ability to fully melt the metal material into a solid 3Dpart. A combination of direct drive motors and mirrors, rather thanfixed optical lens, may be employed. An inert atmosphere is usuallyemployed. A vacuum chamber can be fully purged between build cycles,allowing for lower oxygen concentrations and reduced gas leakage.

Electron beam melting uses a heated powder bed of metal that is thenmelted and formed layer by layer, in a vacuum, using an electron beamenergy source similar to that of an electron microscope. Metal powder iswelded together, layer by layer, under vacuum.

Laser engineering net shaping is a powder-injected technique operates byinjecting metal powder into a molten pool of metal using a laser as theenergy source. Laser engineered net shaping is useful for fabricatingmetal parts directly from a computer-aided design solid model by using ametal powder injected into a molten pool created by a focused,high-powered laser beam. Laser engineered net shaping is similar toselective laser sintering, but the metal powder is applied only wherematerial is being added to the part at that moment. Note that “netshaping” is meant to encompass “near net” fabrication.

Direct metal laser sintering process works by melting fine powders ofmetal in a powder bed, layer by layer. A laser supplies the necessaryenergy and the system operates in a protective atmosphere, typically ofnitrogen or argon.

Another approach utilizes powder injection to provide the material to bedeposited. Instead of a bed of powder that is reacted with an energybeam, powder is injected through a nozzle that is then melted to depositmaterial. The powder may be injected through an inert carrier gas or bygravity feed. A separate shielding gas may be used to protect the moltenmetal pool from oxidation.

Directed energy deposition utilizes focused energy (either an electronbeam or laser beam) to fuse materials by melting as the material isbeing deposited. Powder or wire feedstock can be utilized with thisprocess. Powder-fed systems, such as laser metal deposition and laserengineered net shaping, blow powder through a nozzle, with the powdermelted by a laser beam on the surface of the part. Laser-based wirefeedsystems, such as laser metal deposition-wire, feed wire through a nozzlewith the wire melted by a laser, with inert gas shielding in either anopen environment (gas surrounding the laser), or in a sealed gasenclosure or chamber.

Some embodiments utilize wire feedstock and an electron beam heat sourceto produce a near-net shape part inside a vacuum chamber. An electronbeam gun deposits metal via the wire feedstock, layer by layer, untilthe part reaches the desired shape. Then the part optionally undergoesfinish heat treatment and machining. Wire can be preferred over powderfor safety and cost reasons.

Herderick, “Additive Manufacturing of Metals: A Review,” Proceedings ofMaterials Science and Technology 2011, Additive Manufacturing of Metals,Columbus, Ohio, 2011, is hereby incorporated by reference herein for itsteaching of various additive manufacturing techniques.

FIG. 2 is a flowchart for an exemplary process 200 for producing anadditively manufactured metal component, in some embodiments. In step210, a metal-containing feedstock containing a high-vapor-pressure metalis provided. In step 220, an amount of metal-containing feedstock isexposed to an energy source for melting, thereby generating a jth meltlayer (j=1 to n; n>1). In step 220, a fraction of high-vapor-pressuremetal, or multiple high-vapor-pressure metals, vaporizes away. In step240, the jth melt layer is solidified, thereby generating a jth solidlayer. Steps 220 and 240 each are repeated n times (repeat loop 230),where n is an integer that is at least 2, to produce n individual solidlayers. Step 250 recovers the additively manufactured metal componentwhich contains n solid layers.

The process 200 is not limited in principle to the number of solidlayers that may be fabricated. A “plurality of solid layers” (n in FIG.2) means at least 2 layers, such as at least 10 individual solid layersin the additively manufactured, nanofunctionalized metal alloy. Thenumber of solid layers may be much greater than 10, such as about 100,1000, 10000, or more. The plurality of solid layers may be characterizedby an average layer thickness of at least 10 microns, such as about 10,20, 30, 40, 50, 75, 100, 150, or 200 microns.

The first solid layer, and additional solid layers, may be characterizedby an average grain size of less than 1 millimeter, less than 100microns, less than 10 microns, or less than 1 micron. In variousembodiments, the additively manufactured metal component, or layerswithin it, may be characterized by an average grain size of about, orless than about, 500 microns, 400 microns, 300 microns, 200 microns, 100microns, 50 microns, 25 microns, 10 microns, 5 microns, 2 microns, 1micron, 0.5 microns, 0.2 microns, or 0.1 microns.

In any of these additive manufacturing techniques, post-productionprocesses such as heat treatment, light machining, surface finishing,coloring, stamping, or other finishing operations may be applied. Also,several additive manufactured parts may be joined together chemically orphysically to produce a final object.

Metal alloy systems that utilize grain refiners give a uniquemicrostructure for the additively manufactured metal component. Thegrain refiners may be designed with specific compositions for a givenmetal alloy, taking into account the metal vapor pressures according tothe principles taught herein.

In some embodiments of the invention, the metal-containing feedstockfurther comprises grain-refining nanoparticles. The grain-refiningnanoparticles may be present from about 0.001 wt % to about 10 wt % ofthe metal-containing feedstock, for example. In various embodiments, thegrain-refining nanoparticles are present at a concentration of about0.01 wt %, 0.1 wt %, 1 wt %, or 5 wt % of the metal-containingfeedstock.

Nanoparticles are particles with the largest dimension between about 1nm and about 5000 nm. A preferred size of nanoparticles is about 2000 nmor less, about 1500 nm or less, or about 1000 nm or less. In someembodiments, nanoparticles are at least 50 nm in size.

In these embodiments, the grain-refining nanoparticles are selected fromthe group consisting of zirconium, silver, lithium, manganese, iron,silicon, vanadium, scandium, yttrium, niobium, tantalum, titanium,nitrogen, hydrogen, carbon, boron, and combinations thereof, such asintermetallics or nitrides, hydrides, carbides, or borides of one ormore of the recited metals. In certain embodiments, the grain-refiningnanoparticles are selected from the group consisting of zirconium,titanium, tantalum, niobium, and oxides, nitrides, hydrides, carbides,or borides thereof, and combinations of the foregoing.

Grain-refining nanoparticles, in certain embodiments, are selected fromthe group consisting of Al₃Zr, Al₃Ta, Al₃Nb, Al₃Ti, TiB, TiB₂, WC, AlB,and combinations thereof. These multicomponent nanoparticles may be inplace of, or in addition to, elemental forms such as zirconium,tantalum, niobium, titanium, or oxides, nitrides, hydrides, carbides, orborides thereof.

In some embodiments, micropowders are functionalized with assemblednanoparticles that are lattice-matched to a primary or secondarysolidifying phase in the parent material, or that may react withelements in the micropowder to form a lattice-matched phase to a primaryor secondary solidifying phase in the parent material. In certainembodiments, mixtures of assembled nanoparticles may react with eachother or in some fashion with the parent material, to form alattice-matched material having the same or similar function. Forexample, alloy powder feedstock particles may be mixed withlattice-matched nanoparticles that heterogeneously nucleate the primaryequilibrium phases during cooling of the melt pool. The same concept maybe applied to nanofunctionalized metal precursors besides powders (e.g.,wires).

In some embodiments, the grain-refining nanoparticles arelattice-matched to within ±5% compared to an otherwise-equivalent metalalloy containing the one or more metals but not the grain-refiningnanoparticles. In certain embodiments, the grain-refining nanoparticlesare lattice-matched to within ±2% or within ±0.5% compared to a metalalloy containing the one or more metals but not the grain-refiningnanoparticles.

In some embodiments, the metal-containing feedstock containsmicroparticles that are surface-functionalized with grain-refiningnanoparticles, which may or may not include high-vapor-pressure metals.Surface functionalization may be in the form of a continuous coating oran intermittent coating. A continuous coating covers at least 90% of thesurface, such as about 95%, 99%, or 100% of the surface (recognizingthere may be defects, voids, or impurities at the surface). Anintermittent coating is non-continuous and covers less than 90%, such asabout 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 2%, 1%, or less of thesurface. An intermittent coating may be uniform (e.g., having a certainrepeating pattern on the surface) or non-uniform (e.g., random).

Various coating techniques may be employed, such as (but not limited to)electroless deposition, immersion deposition, or solution coating. Thecoating thickness is preferably less than about 20% of the underlyingparticle diameter, such as less than 15%, 10%, 5%, 2%, or 1% of theunderlying particle diameter.

In general, a functionalization coating may be continuous ordiscontinuous. The coating may have several characteristic features. Inone embodiment, the coating may be smooth and conformal to theunderlying surface. In another embodiment, the coating may be nodular.The nodular growth is often characteristic of kinetic limitations ofnanoparticle assembly. For example, the coating may look likecauliflower or a small fractal growing from the surface. These featurescan be affected by the underling materials, the method of coating,reaction conditions, etc.

Nanoparticles may be attached to particles using electrostatic forces,Van der Waals forces, chemical bonds, physical bonds, and/or any otherforce. A chemical bond is the force that holds atoms together in amolecule or compound. Electrostatic and Van der Waals forces areexamples of physical forces that can cause bonding. A physical bond is abond that arises when molecular entities become entangled in space.Typically, chemical bonds are stronger than physical bonds. Chemicalbonds may include ionic bonds, covalent bonds, or a combination thereof.

Methods of producing nanofunctionalized metals are generally not limitedand may include immersion deposition, electroless deposition, vaporcoating, solution/suspension coating of particles with or withoutorganic ligands, utilizing electrostatic forces and/or Van der Waalsforces to attach particles through mixing, and so on. U.S. patentapplication Ser. No. 14/720,757 (filed May 23, 2015), U.S. patentapplication Ser. No. 14/720,756 (filed May 23, 2015), and U.S. patentapplication Ser. No. 14/860,332 (filed Sep. 21, 2015), each commonlyowned with the assignee of this patent application, are herebyincorporated by reference herein. These disclosures relate to methods ofcoating certain materials onto micropowders, in some embodiments.

When grain-refining nanoparticles are included in the metal-containingfeedstock, the additively manufactured solid layers may have amicrostructure with equiaxed grains. The additively manufactured solidlayers may also be characterized by a crack-free microstructure, inpreferred embodiments (e.g., see FIG. 3B). When there are multiple solidlayers, as is typical, some (but not necessarily all) of the solidlayers may be characterized by an equiaxed-grain microstructure and/or acrack-free microstructure.

A microstructure that has “equiaxed grains” means that at least 90 vol%, preferably at least 95 vol %, and more preferably at least 99 vol %of the metal alloy contains grains that are roughly equal in length,width, and height. In preferred embodiments, at least 99 vol % of themicrostructure contains grains that are characterized in that there isless than 25%, preferably less than 10%, and more preferably less than5% standard deviation in each of average grain length, average grainwidth, and average grain height. Crystals of metal alloy form grains inthe solid. Each grain is a distinct crystal with its own orientation.The areas between grains are known as grain boundaries. Within eachgrain, the individual atoms form a crystalline lattice. In thisdisclosure, equiaxed grains may result when there are many nucleationsites arising from grain-refining nanoparticles contained initially inthe metal-containing feedstock.

By providing a high density of low-energy-barrier heterogeneousnucleation sites ahead of the solidification front, the critical amountof undercooling needed to induce equiaxed growth is decreased. Thisallows for a fine equiaxed grain structure that accommodates strain andprevents cracking under otherwise identical solidification conditions.Additive manufacturing of previously unattainable high-performancealloys, such as Al 7075 or Al 6061, is made possible with improvedproperties over currently available systems.

Preferably, the microstructure of the additively manufactured metalcomponent is substantially crack-free. In certain embodiments, themicrostructure is also substantially free of porous void defects.

A microstructure that is “substantially crack-free” means that at least99.9 vol % of the metal component or layer contains no linear ortortuous cracks that are greater than 0.1 microns in width and greaterthan 10 microns in length. In other words, to be considered a crack, adefect must be a void space that is at least 0.1 microns in width aswell as at least 10 microns in length. A void space that has a lengthshorter than 10 microns but larger than 1 micron, regardless of width,can be considered a porous void (see below). A void space that has alength of at least 10 microns but a width shorter than 0.1 microns is amolecular-level gap that is not considered a defect.

Typically, a crack contains open space, which may be vacuum or maycontain a gas such as air, CO₂, N₂, and/or Ar. A crack may also containsolid material different from the primary material phase of the metalalloy. These sorts of cracks containing material (other than gases) maybe referred to as “inclusions.” The non-desirable material disposedwithin the inclusion may itself contain a higher porosity than the bulkmaterial, may contain a different crystalline (or amorphous) phase ofsolid, or may be a different material altogether, arising fromimpurities during fabrication, for example. Large phase boundaries canalso form inclusions. Note that these inclusions are different than thenanoparticle inclusions that are desirable for grain refining.

The metal component microstructure may be substantially free of porousdefects, in addition to being substantially crack-free. “Substantiallyfree of porous defects” means at least 99 vol % of the additivelymanufactured metal component contains no porous voids having aneffective diameter of at least 1 micron.

Porous defects may be in the form of porous voids. Typically, a porousvoid contains open space, which may be vacuum or may contain a gas suchas air, CO₂, N₂, and/or Ar. Preferably, at least 80 vol %, morepreferably at least 90 vol %, even more preferably at least 95 vol %,and most preferably at least 99 vol % of the additively manufacturedmetal component contains no porous voids having an effective diameter ofat least 1 micron. A porous void that has an effective diameter lessthan 1 micron is not typically considered a defect, as it is generallydifficult to detect by conventional non-destructive evaluation. Alsopreferably, at least 90 vol %, more preferably at least 95 vol %, evenmore preferably at least 99 vol %, and most preferably at least 99.9 vol% of the additively manufactured metal component contains no largerporous voids having an effective diameter of at least 5 microns. Forexample, see the microstructure of FIG. 3B which contains porous voids(but contains no cracks).

The present invention also provides an additively manufactured metalcomponent produced by a process comprising:

(a) providing a metal-containing feedstock comprising ahigh-vapor-pressure metal and at least one other metal species differentthan the high-vapor-pressure metal;

(b) exposing a first amount of the metal-containing feedstock to anenergy source for melting the first amount of the metal-containingfeedstock, thereby generating a first melt layer;

(c) solidifying the first melt layer, thereby generating a first solidlayer of an additively manufactured metal component; and

(d) repeating steps (b) and (c) a plurality of times to generate aplurality of solid layers by sequentially solidifying a plurality ofmelt layers in an additive-manufacturing build direction,

wherein the metal-containing feedstock contains a higher concentrationof the high-vapor-pressure metal compared to the concentration of thehigh-vapor-pressure metal in the solid layers.

In some embodiments, an enrichment ratio of wt % concentration of thehigh-vapor-pressure metal in the metal-containing feedstock to wt %concentration of the high-vapor-pressure metal in the first solid layeris at least 1.05, at least 1.25, at least 1.5, or at least 2.0.

In the additively manufactured metal component, the high-vapor-pressuremetal may be selected from the group consisting of Mg, Zn, Li, Al, Cd,Hg, K, Na, Rb, Cs, Mn, Be, Ca, Sr, Ba, and combinations thereof.

In certain additively manufactured aluminum components, themetal-containing feedstock contained Al, from 0.05 wt % to 0.28 wt % Cr,from 1 wt % to 2 wt % Cu, from 3 wt % to 10 wt % Mg, and from 6.2 wt %to 20 wt % Zn; and the first solid layer and/or additional solid layerscontain(s) Al, from 0.18 wt % to 0.28 wt % Cr, from 1.2 wt % to 2 wt %Cu, from 2.1 wt % to 2.9 wt % Mg, and from 5.1 wt % to 6.1 wt % Zn.

In certain additively manufactured aluminum components, themetal-containing feedstock contained Al, from 0.01 wt % to 5 wt % Zr,from 1 wt % to 2.6 wt % Cu, from 2.7 wt % to 10 wt % Mg, and from 6.7 wt% to 20 wt % Zn; and the first solid layer and/or additional solidlayers contain(s) Al, from 0.08 wt % to 5 wt % Zr, from 2 wt % to 2.6 wt% Cu, from 1.9 wt % to 2.6 wt % Mg, and from 5.7 wt % to 6.7 wt % Zn.

In certain additively manufactured aluminum components, themetal-containing feedstock contained Al, from 0.01 wt % to 5 wt % Zr,from 1.9 wt % to 10 wt % Mg, and from 7.1 wt % to 20 wt % Zn; and thefirst solid layer and/or additional solid layers contain(s) Al, from0.07 wt % to 5 wt % Zr, from 1.3 wt % to 1.8 wt % Mg, and from 7 wt % to8 wt % Zn.

The additively manufactured metal component may be characterized by anaverage grain size of less than 1 millimeter, such as less than 100microns, less than 10 microns, or less than 1 micron.

In some embodiments, the additively manufactured metal component has amicrostructure with a crystallographic texture that is not solelyoriented in the additive-manufacturing build direction. The plurality ofsolid layers may have differing primary growth-direction angles withrespect to each other.

In some embodiments, the additively manufactured metal component has amicrostructure with equiaxed grains. In some embodiments, the additivelymanufactured metal component has a crack-free microstructure. In certainembodiments, the additively manufactured metal component has acrack-free microstructure with equiaxed grains.

Variations of the present invention also provide a metal-containingfeedstock for additive manufacturing or for welding, wherein themetal-containing feedstock contains at least one high-vapor-pressuremetal, and wherein concentration of the high-vapor-pressure metal(s) inthe metal-containing feedstock is selected based on a desiredconcentration of the high-vapor-pressure metal in an additivelymanufactured metal component derived from the metal-containingfeedstock. The concentration of the high-vapor-pressure metal will behigher (enriched) in the metal-containing feedstock, compared to thefinal additively manufactured or welded metal component. The enrichmentratio of wt % concentration of the high-vapor-pressure metal in themetal-containing feedstock to wt % concentration of thehigh-vapor-pressure metal in the final additively manufactured or weldedmetal component is typically at least 1.05, such as at least 1.25, atleast 1.5, or at least 2.0.

Some embodiments provide a metal-containing feedstock for additivemanufacturing or welding of an aluminum component, containing from 0.05wt % to 0.28 wt % Cr, from 1 wt % to 2 wt % Cu, from 3 wt % to 10 wt %Mg, and from 6.2 wt % to 20 wt % Zn, with the balance consistingessentially of aluminum. Other elements may be present, such as (but notlimited to) Zr, Ag, Li, Mn, Fe, Si, V, Sc, Y, Nb, Ta, Ti, B, H, C,and/or N.

Other embodiments of the invention provide a metal-containing feedstockfor additive manufacturing or welding of an aluminum component, whereinthe metal-containing feedstock contains from 0.01 wt % to 5 wt % Zr,from 1.9 wt % to 10 wt % Mg (such as from 2.7 wt % to 10 wt % Mg), andfrom 6.7 wt % to 20 wt % Zn (such as from 7.1 wt % to 20 wt % Zn), withthe balance consisting essentially of aluminum. In some embodiments, themetal-containing feedstock further contains from 1 wt % to 2.6 wt % Cu.Other elements may be present, such as (but not limited to) Cr, Cu, Ag,Li, Mn, Fe, Si, V, Sc, Y, Nb, Ta, Ti, B, H, C, and/or N.

The materials and methods disclosed herein may be applied to additivemanufacturing as well as joining techniques, such as welding. Certainunweldable metals, such as high-strength aluminum alloys (e.g., aluminumalloys Al 7075, Al 7050, or Al 2199) would be excellent candidates foradditive manufacturing but normally suffer from hot cracking. Theprinciples disclosed herein allow these alloys, and many others, to beprocessed with significantly reduced cracking tendency.

Certain embodiments relate specifically to additive manufacturing ofaluminum alloys. Additive manufacturing has been previously limited toweldable or castable alloys of aluminum. This disclosure enablesadditive manufacturing of a variety of high-strength and unweldablealuminum alloys by utilizing grain refinement to induce equiaxedmicrostructures which can eliminate hot cracking during processing.Potential applications include improved tooling, replacement of steel ortitanium components at lower weight, full topological optimization ofaluminum components, low-cost replacement for out-of-productioncomponents, and replacement of existing additively manufactured aluminumsystems.

Some embodiments of the present invention utilize materials, methods,and principles described in commonly owned U.S. patent application Ser.No. 15/209,903, filed Jul. 14, 2016, U.S. patent application Ser. No.15/808,872, filed Nov. 9, 2017, U.S. patent application Ser. No.15/808,877, filed Nov. 9, 2017, and/or U.S. patent application Ser. No.15/808,878, filed Nov. 9, 2017, each of which is hereby incorporated byreference herein. For example, certain embodiments utilizefunctionalized powder feedstocks as described in U.S. patent applicationSer. No. 15/209,903. The present disclosure is not limited to thosefunctionalized powders. This specification also hereby incorporates byreference herein Martin et al., “3D printing of high-strength aluminiumalloys,” Nature vol. 549, pages 365-369 and supplemental online content(extended data), Sep. 21, 2017, in its entirety.

Some variations provide a method of making a welded metal component, themethod comprising:

(a) providing a metal-containing feedstock comprising ahigh-vapor-pressure metal and at least one other metal species differentthan the high-vapor-pressure metal;

(b) exposing an amount of the metal-containing feedstock to an energysource for melting the amount of the metal-containing feedstock, therebygenerating a melt layer; and

(c) solidifying the melt layer, thereby generating a solid layer of awelded metal component,

wherein the metal-containing feedstock contains a higher concentrationof the high-vapor-pressure metal compared to the concentration of thehigh-vapor-pressure metal in the solid layer.

Some variations also provide a welded metal component produced by aprocess comprising:

(a) providing a metal-containing feedstock comprising ahigh-vapor-pressure metal and at least one other metal species differentthan the high-vapor-pressure metal;

(b) exposing an amount of the metal-containing feedstock to an energysource for melting the amount of the metal-containing feedstock, therebygenerating a melt layer; and

(c) solidifying the melt layer, thereby generating a solid layer of awelded metal component;

wherein the metal-containing feedstock contains a higher concentrationof the high-vapor-pressure metal compared to the concentration of thehigh-vapor-pressure metal in the solid layer.

The final additively manufactured component may have porosity from 0% toabout 75%, such as about 5%, 10%, 20%, 30%, 40%, 50%, 60%, or 70%, invarious embodiments. The porosity may derive from space both withinparticles (e.g., hollow shapes) as well as space outside and betweenparticles. The total porosity accounts for both sources of porosity.

The final additively manufactured or welded component may be selectedfrom the group consisting of a structure, a coating, a geometric object,a billet, an ingot (which may be a green body or a finished body), anet-shape part, a near-net-shape part, a welding filler, andcombinations thereof. Essentially, the geometry of an additivemanufacturing part is unlimited.

In some embodiments, the additively manufactured or welded component hasa density from about 1 g/cm³ to about 20 g/cm³, such as about 2, 3, 4,5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 g/cm³.

Some possible powder metallurgy processing techniques that may beapplied to the additive manufactured or welded component include hotpressing, cold pressing, low-pressure sintering, extrusion, pressurelesssintering, and metal injection molding, for example. Melting may includeinduction melting, resistive melting, skull melting, arc melting, lasermelting, electron beam melting, semi-solid melting, or other types ofmelting (including conventional and non-conventional melt processingtechniques). Casting may include centrifugal, pour, or gravity casting,for example. Sintering may include spark discharge,capacitive-discharge, resistive, or furnace sintering, for example.Mixing may include convection, diffusion, shear mixing, or ultrasonicmixing, for example.

Optionally, porosity may be removed or reduced in the final component.For example, a secondary heat and/or pressure (or other mechanicalforce) treatment may be done to minimize porous voids present in anadditively manufactured component. Also, pores may be removed from theadditively manufactured component by physically removing (e.g., cuttingaway) a region into which porous voids have segregated.

In addition to removal of voids, other post-working may be carried out.For example, forging can refine defects and can introduce additionaldirectional strength, if desired. Preworking (e.g., strain hardening)can be done such as to produce a grain flow oriented in directionsrequiring maximum strength.

In this detailed description, reference has been made to multipleembodiments and to the accompanying drawings in which are shown by wayof illustration specific exemplary embodiments of the invention. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatmodifications to the various disclosed embodiments may be made by askilled artisan.

Where methods and steps described above indicate certain eventsoccurring in certain order, those of ordinary skill in the art willrecognize that the ordering of certain steps may be modified and thatsuch modifications are in accordance with the variations of theinvention. Additionally, certain steps may be performed concurrently ina parallel process when possible, as well as performed sequentially.

All publications, patents, and patent applications cited in thisspecification are herein incorporated by reference in their entirety asif each publication, patent, or patent application were specifically andindividually put forth herein.

The embodiments, variations, and figures described above should providean indication of the utility and versatility of the present invention.Other embodiments that do not provide all of the features and advantagesset forth herein may also be utilized, without departing from the spiritand scope of the present invention. Such modifications and variationsare considered to be within the scope of the invention defined by theclaims.

What is claimed is:
 1. An aluminum alloy feedstock for additivemanufacturing, said aluminum alloy feedstock comprising: from 81.5 wt %to 88.8 wt % aluminum; from 1.1 wt % to 2.1 wt % copper; from 3.0 wt %to 4.6 wt % magnesium; and from 7.1 wt % to 9.0 wt % zinc.
 2. Thealuminum alloy feedstock of claim 1, wherein said aluminum alloyfeedstock is in the form of a powder.
 3. The aluminum alloy feedstock ofclaim 1, wherein said aluminum alloy feedstock is in the form of afeedstock ingot.
 4. The aluminum alloy feedstock of claim 1, whereinsaid aluminum alloy feedstock comprises from 0.005 wt % to 0.4 wt %silicon.
 5. The aluminum alloy feedstock of claim 1, wherein saidaluminum alloy feedstock comprises from 0.005 wt % to 0.4 wt % iron. 6.The aluminum alloy feedstock of claim 1, wherein said aluminum alloyfeedstock comprises from 0.005 wt % to 0.3 wt % manganese.
 7. Thealuminum alloy feedstock of claim 1, wherein said aluminum alloyfeedstock comprises from 0.005 wt % to 0.1 wt % chromium.
 8. Thealuminum alloy feedstock of claim 1, wherein said aluminum alloyfeedstock comprises from 0.005 wt % to 0.05 wt % nickel.
 9. The aluminumalloy feedstock of claim 1, wherein said aluminum alloy feedstockcomprises from 0.005 wt % to 0.2 wt % titanium.
 10. The aluminum alloyfeedstock of claim 1, wherein said aluminum alloy feedstock comprisesfrom 0.005 wt % to 0.05 wt % tin.
 11. The aluminum alloy feedstock ofclaim 1, wherein said aluminum alloy feedstock comprises: from 84.9 wt %to 88.3 wt % aluminum; from 1.2 wt % to 2.0 wt % copper; from 3.2 wt %to 4.4 wt % magnesium; and from 7.3 wt % to 8.7 wt % zinc.
 12. Thealuminum alloy feedstock of claim 11, wherein said aluminum alloyfeedstock comprises from 0.005 wt % to 0.12 wt % silicon.
 13. Thealuminum alloy feedstock of claim 11, wherein said aluminum alloyfeedstock comprises from 0.005 wt % to 0.15 wt % iron.
 14. The aluminumalloy feedstock of claim 11, wherein said aluminum alloy feedstockcomprises from 0.005 wt % to 0.1 wt % manganese.
 15. The aluminum alloyfeedstock of claim 11, wherein said aluminum alloy feedstock comprisesfrom 0.005 wt % to 0.05 wt % chromium.
 16. The aluminum alloy feedstockof claim 11, wherein said aluminum alloy feedstock comprises from 0.005wt % to 0.05 wt % nickel.
 17. The aluminum alloy feedstock of claim 11,wherein said aluminum alloy feedstock comprises from 0.005 wt % to 0.1wt % titanium.
 18. The aluminum alloy feedstock of claim 11, whereinsaid aluminum alloy feedstock comprises from 0.005 wt % to 0.05 wt %tin.
 19. The aluminum alloy feedstock of claim 1, wherein said aluminumalloy feedstock consists essentially of said aluminum, said copper, saidmagnesium, and said zinc.